James W. Truran

The collapse of our Galaxy and the formation of the Galactic disk

The self-regulated chemical and dynamical evolution of an initially hot, gaseous protodisk is examined in detail, taking into account both star formation and heating and cooling processes in a multicomponent interstellar medium. It is shown that one can understand the observed structure of the galactic disk in a natural way as a consequence of the gravitational settling of the protodisk. During the first 4-6 × 10 9 yr, stars form in a thick disk and «old thin disk» component, with kinematical and chemical properties which are in agreement with the observations

The recurrent nova U Scorpii revisited - Can a certain class of models be eliminated

Theoretical models for the recurrent nova U Sco are identified and discussed. In particular, the possible relevance of disk instability models are examined when account is taken of the helium-rich character of the material observed in the disk in quiescence. Even with the assumption of a pure helium disk, it is concluded that it is extremely unlikely that the outbursts of U Sco (and the very similar recurrent nova V394 CrA) are attributable to a disk instability. 31 refs.

The influence of our Galaxy on the evolution of the Magellanic Clouds

Building upon the assumption of the existence of a hot gaseous corona around the Milky Way Galaxy and a calculation of possible past orbits of the Magellanic Clouds in the gravitational potential of the Galaxy, the question as to whether significant interchange of material could have occurred with the Large Magellanic Cloud is examined. It is estimated that, indeed, the LMC could have exchanged a nontrivial fraction, of the order of 30 percent, of its mass with the corona, over an assumed 10 to the 10th yr of interaction. It therefore follows that, if the Clouds were bound to the Galaxy during the past 10 to the 10th yr, their chemical and dynamical histories would have been strongly influenced by those of the Galaxy itself. It is concluded that either (1) the Clouds have not been bound to the Galaxy over most of its 10 to the 10th yr lifetime, or (2) it is not possible to treat their evolutions as those of isolated systems. 32 refs.