Summary

The major conclusions of this paper are as follows:

1.

The Milky Way is a significant evolutionary driver of LMC structure. The time-dependent tidal forcing by the Milky Way will heat the LMC disk, producing extended rotating spheroid component.

2.

We find that the disk scale height increases at a rate of $70{\rm\,pc}/{\rm\,Gyr}$ (cf. Fig 6). The heating has several components. First, there is a direct resonant coupling between the time dependence of tidal forcing and the stellar orbits within the LMC disk. Second, the body torque from the Milky Way causes the LMC disk to precess. The interaction between the LMC halo and its precessing disk heats the disk. This is a new but important mechanism for heating the disks of satellites.

3.

The stellar velocity dispersion decreases due to disk heating. The work done against the LMC gravitational potential decreases the depth of the potential well and the new quasi-equilibrium, although more extended, requires less velocity support. The sign of the effect follows from the virial theorem. Although a surprise to some, this effect has been well-documented for the evolution of star clusters.

4.

The mass loss rate is approximately $3\times10^8{\rm\,M_\odot}$ per orbit or roughly 2% per orbit at the current time. The fraction of halo loss to disk loss is roughly 3:1.

5.

Because the heated, extended component is preferentially lost to tidal stripping, the unbound stars will not be distributed like the Magellanic gas stream but in a diffuse distribution about the LMC. This component may be a source of both microlensing sources and lenses and affect MACHO estimates. Overall, we estimate that the heated disk and tidally stripped component may make a significant contribution to gravitational microlensing.

I thank Neal Katz and Sergei Nikolaev for many useful discussions and Neal Katz and Eric Linder for comments on the manuscript. This work described here was supported in part by NSF AST-9529328 and NASA/JPL 961055.