Dynamical Models of Novae

The dynamics of a nova outburst are studied by means of a time-dependent hydrodynamics computer program which includes transport of energy by radiation and convection. Two distinct types of ejections which could give rise to novae are identified. The "flash" nova (e g., T CrB) has a very rapidly rising and falling light curve and a rapidly decreasing velocity curve. A strong shock wave which imparts a velocity greater than the escape velocity to the outer layers of the star will produce this behavior. A less rapidly rising and falling light curve and a nearly constant velocity are characteristic of the "ordinary" nova (e.g., GK Per). These features will result when the stellar material is forced outward by a pressure front which is not a shock wave. The pre-maximum halt, which is characteristic of the latter type of nova, results from the temperature dependence of the opacity of neutral hydrogen