THE 8190-ANGSTROM SODIUM DOUBLET IN CATACLYSMIC VARIABLES .4. A SURVEY OF 22 OBJECTS

A survey of 22 known and suspected cataclysmic variables has been carr ied out with the 4.2-m WHT on La Palma, using ISIS to provide coverage of most of the optical spectrum. 10 faint stars (UU Aql, AT Cnc, EY C yg, CG Dra, LL Lyr, NN Ser, BC UMa, DV UMa, TW Vir and REJ1629+780) an d one bright one (Z Cam) show red dwarf features in the spectrum. For UU Aql, EY Cyg, LL Lyr and TW Vir, this is the first direct spectrosco pic detection of the red dwarf. For all these systems we have determin ed the most probable spectral type of the secondary star. In addition we find marginal evidence of the red dwarf in V391 Lyr, SW UMa and PQ Gem (=REJ0751 + 144). Allowing for selection effects, the proportion o f systems that show evidence of the red dwarf is larger than that foun d in an earlier survey of brighter objects.