Shaping of nova remnants by binary motion

We present the results of 2.5D hydrodynamic calculations of the effects of the underlying binary system on shaping the ejecta in a classical nova outburst. In the model, the outburst takes place in the form of a wind with secularly increasing velocity. This wind flows past a binary companion, which experiences a frictional drag force and transfers energy and angular momentum from its orbit into the expanding envelope. We find that many of the features seen in classical novaremnants can be reproduced, including polar blobs, polar rings and shells with tropical and equatorial bands. The features seen in the shells correlate with speed class in the observed manner — fast novae produce spherical shells, whereas slower novae produce banded shells and polar blobs. The effects of radiative cooling andthe Rayleigh-Taylor instability on the shells are discussed. It is found that, as observations appear to indicate, the shells of fast novae should comprise a few, large clumps, whereas the shells of slower novae will be clumped on scales which are small compared to the shell radius.