The spectra of novae

Abstract

Typical novae have four systems of absorption lines. In chronological order of appearance, as well as of increasing displacement, these are: (1) pre-maximum; (2) principal; (3) diffuse enhanced; (4) Orion. The principal system lies on the short wavelength edges of a strong set of wide, undisplaced emission lines. Structures appear early in the emission and can be correlated with local knots in the expanding nebulae years later. Diffuse enhanced and Orion lines also have associated, but more vague, emission.Secondary variations of light are correlated with spectral changes. With a re-brightening, the spectrum reverts to a stage already passed. Variations of line displacements accompany these changes. For Orion lines the oscillations are considered real, and due to variable speed of ejection. In the diffuse enhanced system, apparent oscillations are due mainly to variable strength of blended, multiple lines. Critical examination fails to confirm supposed rapid gravitational retardation of gases.Recurrent novae form a special problem. Some, at least, fail to fit the typical pattern. Old novae, and probably pre-nova stars as well, are hot subdwarfs.