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K. E. Belle, C. E. Woodward (University of Wyoming), A. Evans, S. Eyres (University of Keele), R. D. Gehrz, M. Schuster (University of Minnesota), M. A. Greenhouse (NASA Goddard), J. Krautter (Landessternwarte), S. G. Starrfield (Arizona State University), J. Truran (University of Chicago)
Novae are remarkable laboratories in which several poorly understood astrophysical processes, many not specific to novae - such as the physics of hot dense winds, dust formation and common envelope evolution - can be studied in real time. Of particular importance is the study of the nova shell which is formed by the ejecta. The resolved remnant yields clues about other aspects of nova physics: it is now well established that nova shells are not spherically symmetric. They show a very complicated structure consisting of many individual emission knots and streamers that temporally evolve. The actual geometry of the ejected shell carries information about the inclination of the underlying binary and the physics of the common envelope phase, when the binary is engulfed by the ejected material. There are also indications of possible abundance gradients in nova ejecta. This may point either to the fact that the TNR which gave rise to the eruption may not have been spherically symmetric, or it may merely indicate that excitation conditions vary across the nebula (for example, as a result of an inhomogeneous radiation field).
We present initial results of our HST/NICMOS multiwavelength imaging study of the novae QU Vul (1984), QV Vul (1987), V1974 Cyg (1992), and V723 Cas (1995). These four novae exhibit a wide variety of individual properties such as ONeMg vs. CO nova, fast vs. slow nova, dust formation vs. no dust formation.
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