THE COMPANION OF THE CLASSICAL CEPHEID Z-LACERTAE

A deep IUE exposure of the Cepheid Z Lacertae from 1200 to 2000 angstr om has been taken in order to search for light from the radial-velocit y companion. A faint signal of approximately 1.0 X 10(-14) ergs angstr om-1 s-1 cm-2 has been detected in the dereddened spectrum. Because th is is approximately the flux expected due to ''camera artifacts,'' we consider that at least part of this signal does not come from Z Lac B. We use this flux as an upper limit to the flux of the companion. This corresponds to a spectral type later than A5 V at the distance of the Cepheid. We have also obtained new radial-velocity observations of Z Lac. Although only limited velocity data are available, an orbital-vel ocity variation of 16 km s-1 has been observed. Combining this with ev en the shortest period compatible with the data (approximately 14 yr) implies a much more massive companion than is seen in the IUE spectrum . It is likely that the companion is itself a binary.