Spectroscopy and spectrophotometry of cataclysmic variable stars

Distances and luminosities of individual cataclysmic variable stars (as opposed to statistical properties of the group as a whole) can best be acquired by studying the secondary stars of these short-period binary systems. Since the secondary stars are of late spectral type, observations in the near infrared are especially useful. A spectrophotometric survey of about 30 cataclysmic variable stars has been carried out from 0.3μ to 1μ. Old novae, nova-like variables, and erupting dwarf novae are characterized by spectral energy distributions which are flat (f/sub v/ = constant) or rising toward shorter wavelengths. These objects have Balmer jumps in absorption or else no Balmer jump at all. No trace of a red stellar spectrum is evident in these stars, except for the nova-like system RW Tri. These spectral energy distributions are analyzed to determine the spectral types of the secondary stars and the fraction of light contributed by the primary stars and their accretion disks. The analysis makes use of flux-ratio diagrams to eliminate those spectral decompositions which result in physically implausible energy distributions for the accretion disks. The Balmer jump is especially useful in eliminating unphysical distributions. It is argued that the secondary stars in cataclysmic variable systems should be expected to deviate from the normal main-sequence relations among mass, radius, spectral type, and luminosity